Multicore Fibers

Overcoming the limits of communication capacity

Advances in AI and cloud services are driving a continuous increase in the volume of data transmitted over optical networks, especially submarine cables linking data centers. Traditional single-mode optical fibers, which contain only one transmission core per fiber, have reached their capacity limit.

To overcome this, Space Division Multiplexing (SDM) is being considered as a promising solution.

A key example of SDM is the multicore fiber (MCF), which integrates multiple independent cores into a single fiber. The industry is now actively pursuing the development of this technology. There are two types of MCFs: strongly coupled and weakly coupled. Of these, the weakly coupled type is particularly promising, as it minimizes interference between cores and enables both stable signal quality and high-capacity transmission.

Applications of MCF

MCFs are being considered for application to a wide range of fields, including telecommunications and sensing technologies. In fact, proof-of-concept trials are already underway for submarine optical networks.

Submarine Optical Networks

Data Center Interconnect (DCI)

Core/Metro Networks

MCF Testing Challenges

MCFs are known to be significantly affected by inter-core crosstalk, which can degrade transmission quality. Inter-core crosstalk occurs when an optical signal traveling through one core leaks into an adjacent core, causing interference to its signal. As crosstalk increases, the Optical Signal-to-Noise Ratio (OSNR) decreases, leading to poorer communication quality.

To ensure high-quality transmission, it is essential to accurately evaluate the crosstalk characteristics. Furthermore, identifying the factors that cause crosstalk variations during the design, manufacturing, and operational stages is key to maintaining stable long-term performance.

Multicore Fiber Testing Solution

The Multi Channel Fiber Tester MT9100A is the industry's first OTDR* capable of evaluating the transmission quality of MCFs. This standalone device can precisely visualize not only transmission loss and reflection, but also inter-core crosstalk along the length of the fiber. The MT9100A can simultaneously test up to four cores, allowing users to instantly assess transmission characteristics such as crosstalk, fiber breaks, connector losses, and bending issues for each core individually.

The MT9100A provides innovative support for evaluating optical transmission quality at every stage from R&D to network deployment and maintenance. It enables efficient, high-precision inspection and maintenance by simultaneously testing multiple cores at once—there is no need to reconnect individual fibers. With an intuitive user interface and automatic analysis features, even users without specialized knowledge can easily run tests. This greatly reduces the on-site workload and significantly improves operational efficiency.

The MT9100A is the ideal solution to the issues presented by the new MCF era.

*: As of November 2025, based on our internal research.

Resources

White paper space division multiplexing and multicore fibers

White Paper:
Space Division Multiplexing (SDM) Technologies and Multicore Fiber

This white paper provides a clear overview of space division multiplexing technologies, highlighting the key testing challenges associated with multicore optical fibers and presenting the latest approaches to address them.

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